Drilling systems are frequently used to provide cylindrical holes in metallic workpieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto such as the type commonly referred to as a spade-type drill. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.
One problem with prior art spade-type cutting tools is that insert is typically configured as a flat blade and the holder is configured with a straight flute. Even when used with flush channels through the holder, these types of drill assemblies are best suited for drilling shallow holes at relatively slower speeds due to their poor chip removal. Helical flutes are provided in typical twist drills to help in chip removal. Large helix angled flutes (often 20 degrees or above) are used for effective chip removal at high drilling speeds.
Attempts have been made in the prior art to combine the versatility and cost-effectiveness of the spade-type insert and holder with the benefits of helical flutes, however, these efforts have resulted in complex or inadequate blade retaining systems as well as complex shaped blades which negate the cost benefits of the replaceable blade insert. Other prior art attempts have combined a helical flute with a portion of a straight flute at the drill insert connection end in order to accommodate a flat drill insert. However in terms of chip removal, improved performance can be obtained if the helical flute is adjacent the cutting edges. In this prior art configuration, the chips are first transported by a straight portion resulting in loss of efficiency in removing chips and forcing a slower cutting speed for the tool. In addition, the straight cutting edge of the flat cutting blade does not typically dissipate heat as well as a curved cutting edge. If the point does not adequately conduct heat away from its cutting edges, the temperature buildup will “burn” the point and diminish the life of the drill bit. The heat generated at the lip of the drill point is directly related to the load and stresses the lip is subjected to. The more efficiently load stresses are dissipated, the less heat is built up at the cutting edge of the drill point.
Some prior art inserts have been developed with radially curved cutting edges. However, these prior art inserts are apt to direct chips directly into the clamp arms of the holder during operation of the tool. The clamp arms and the holder are made of a steel material that is significantly softer than the hard carbide material typically used to manufacture the drill insert. The chips impacting against the clamp arms erode and wear the clamp arms. This chip erosion of the clamp arms significantly reduces the life of the holder.
Therefore, there remains a need in the art for a drill insert tool that overcomes one or more or the disadvantages identified in the prior art.